Deluxe Electric Mistress trimpots: help!!!!

[Scruffie]

Well something funny is happening here, you say your regulator is giving out 3V, but your opamps are showing they are getting 17V... which is higher than it should be.

The voltages on those look fine other than that, what are your voltages on the 4013, 311, & 324.

The 4558 is biased by the SAD1024 output voltage so for now we'll assume it's not the problem.

Edit: You have checked the pedal is grounded to the enclosure haven't you... that might explain the strange readings, if you use a ground point on the PCB (the middle pin of the regulator would do) for the black lead of your multimeter and check the regulator output that way.

[Fenderstratocaster0]

So this is the regulator i am measuring. Output is 2.7v and input 3.4v. Circled in red.

When I go and use the middle pin ground of this regulator as a reference ground the readings are dropping. So I used the ground of the other 78L15 (not circled in the photo) and it results in the 2.7v and 3.4v which matches when I use the enclosure.

Would there be a problem with this regulator in red? I bought a spare if needed.

4013 voltages

1. 7.3
2. 7.3
3. 7.7
4. 0
5. 7.4
6. 0
7. 0
8. 0
9. 0
10. 0
11. 0
12. 0.02
13. 16.9
14. 16.9

311 voltages

1. 0
2. 3.8
3. 2.7
4. 0
5. 17
6. 17
7. 7.7
8. 16.9

324 voltages

1. Cycling between 0 and 16
2. 7.4
3. Cycling between 4 and 10
4. 16.9
5. 1.95
6. 1.99
7. 3.9
8. Cycling between 0 and 9
9. 7.4
10. 7.4
11. 0
12. 1.9
13. 1.9
14. 1.9

[Rob Strand]

I'm using the V1 schematic from this great collection:
http://www.metzgerralf.de/elekt/stomp/mistress/index.shtml
http://www.metzgerralf.de/elekt/stomp/mistress/images/deluxe-electric-mistress-v1-schematic.gif

I don't see how you can get 17V from a 15V regulator without something being wrong.
Maybe the regulator was installed the wrong way around?

[Rob Strand]

So this is the regulator i am measuring. Output is 2.7v and input 3.4v. Circled in red.

I looked at the PCB and I suspect the part marked with the RED circle is not the regulator.
To me it looks like the lower part nearer to the diodes and the two big caps is the regulator (making the RED circled part the transistor).

[Fenderstratocaster0]

Based on the schematic you mean this?

[Rob Strand]

Based on the schematic you mean this?

Yes.

You should also confirm it yourself like this:
- Look at the schematic find the two diodes on the left.
  Now look at the PCB and find the diodes the transformer wires connect to.
- On the schematic notice the two diodes connect together then connect to the regulator.
  On the PCB find the track where the two diodes connect together then go to the regulator.
  (Confirm also that it goes to the correct pin of the regulator.)

You should also be able to confirm the part number marked on the device.
However, you should check the part via the PCB connections, as I mentioned before.

[Fenderstratocaster0]

Thanks for the help and clarity.

Sorry was my bad on mixing the 2 up and not checking the board clearly.

Okay so the reading on the output are 19.3v and 17.8v input on the regulator.

The transistor is reading at 2.7v output and 3.4v input.

All the voltages posted above are still unchanged for the 4013 and 311 and 324.

Pins 1,3,8 on the 324 do not hold a constant V.

[Rob Strand]

Okay so the reading on the output are 19.3v and 17.8v input on the regulator.

The output at 17.8 volts looks bad it should be 15V.
You could check the soldering on the ground pin of the regulator.  Perhaps touch it up.

The transistor is reading at 2.7v output and 3.4v input.

Not sure what input and output is.
Look here
https://upload.wikimedia.org/wikipedia/commons/4/41/Transistor_PNP_symbol.png

B = base, E = emitter, C = collector.

From what I can see:
- the base should be about 1.5V off the +V rail.
  So for your +V=17.8V,    (Keep in mind +V should be +15V)
  base = 17.8 - 1.5 = 16.3V
- the emitter should be about 0.65 V higher than that. So about 16.3V + 0.65 = 16.95V
- The collector is connected to pin 3 of the LM 311 so that will be at 2.7V based on you previous measurements.
  It looks *roughly* right as it should be close to the voltage on pin 2 of the LM 311 which is 3.8V.
  I would of expected slightly better match but it's not really a place to be probing with a multimeter
and getting a precise value.

So to me, your transistor E and B voltages look wrong.

The other thing to keep in mind is the switch position.  On one position the voltage in pin 3 of the LM311 will be constant on the other it will move around like the LM324 voltages.

Just to clarify something,   before you said you replaced the 78L15  did you put the new regulator in the transistor position or in the regulator position on the PCB?

[Scruffie]

Just to clarify something,   before you said you replaced the 78L15  did you put the new regulator in the transistor position or in the regulator position on the PCB?

What I was about to ask, would explain why you stopped getting audio after replacing it and also probably indicate the regulator is in fact bad if it's putting out 17V.

Other than the supply voltage, the voltages you've posted look within range for the IC's.

[Fenderstratocaster0]

Okay so I definitely replaced the wrong spot. I put the new 78L15 in the spot circled in red.

It should have gone into the spot circled in green.

At this point to correct the issue given the readings being too high I have another 78L15 spare.

Steps should be to swap the new 78L15 in the green circled space.

What about the one in the transistor position I already changed.

Sorry I realize this was a simple mistake and trying not to waste the help I'm getting by misguiding the process I took. I really appreciate the help here!

Thanks to you both!

[Scruffie]

These things happen, even to the best of us, main thing is we've caught it and can carry on debugging.

The transistor you replaced by mistake would have either been a 2N5087 or BC309 (check which as the pinouts are opposite IIRC) either put back the original transistor, you can do a quick and dirty test to see if it gives you a reading on the hFe setting of your multimeter to check it's not fried or replace it with a new one.

If you threw it out you need to check the datasheet for the replacement you get to find out the pinout and then trace the connections vs. the schematic to make sure you orient it correctly.

[Fenderstratocaster0]

I will have to get a replacement 2N5087 as I don't have a spare. Will be delayed till Monday.

Thanks guys!

Also my local electronic store doesn't carry certain items.

Noticed the regulator is a 78L15A.

Am I running any issues replacing with a 78L15. Haven't done it yet.

[Rob Strand]

Here's how I see the transistor orientations.   You pics seems to match the 2N5087 orientation.


You could use any transistor for now just make sure it's in the right way.  The part isn't that critical.

What happened to the old one?  It was probably good.   And the trimpot is set to match that part.
Technically you need to tweak the trim-pot to match the transistor.

Interestingly the schematic shows 62k but the pics seem to have 82k.

[Scruffie]

Interestingly the schematic shows 62k but the pics seem to have 82k.

Definitely looks like 62k on my screen, I have a red light filter though so maybe that's bringing out the colour better.

What happened to the old one?  It was probably good.   And the trimpot is set to match that part.
Technically you need to tweak the trim-pot to match the transistor.

True but with component drift and cap replacements, that probably needed to happen anyway.

[Rob Strand]

Definitely looks like 62k on my screen, I have a red light filter though so maybe that's bringing out the colour better.

Actually when I look at the zoomed image it looks like 62k.  It's definitely a pure blue.

[Fenderstratocaster0]

So

Regulator is now giving reading of 15v input and 22v output.
Transistor is E:14v C:1.5-2.7 cycling.

The regulator was replaced with a 78L15 and original was 78L15A

[Rob Strand]

Regulator is now giving reading of 15v input and 22v output.

22V in and 15V out - yeah?

More importantly is it working?

[Fenderstratocaster0]

So there is now NO signal coming through.

Not even the direct output jack which was working before without issue.

I rechecked that the transformer is still putting out 16v to each cable.

I tried flipping the switch between the filter matrix and flanger and no signal through either.

Not sure how to proceed.

[Rob Strand]

Not sure how to proceed.

If there's no direct signal there's a chance IC1a and/or IC1b is not biased correctly. 
You will find the DC voltage at the output is stuck at the supply rail or ground.
http://www.metzgerralf.de/elekt/stomp/mistress/images/deluxe-electric-mistress-v1-schematic.gif

If the DC at the output of IC1b is off maybe the bias trimpot needs adjusting.   IC1a will probably be off as well.
If only the DC at the output of Ic1a is off then maybe the gain trimpot is off.

[Edit:  Another thing, the cap you replaced, make sure it is in the correct way around.   If it's a tantalum put in the wrong way it will stuff-up the DC voltages.]

[Scruffie]

Rob is right about checking that tantalum polarity, especially as before you replaced it you were getting some signal.

Your IC1 (4558) voltages look okay to me though and I wouldn't touch any of the trim pots just yet, if anything i'd suspect the 741.

I think now it's time to build an audio probe, assuming you don't have a scope you'll need it for re-biasing later on anyway.

But that's excellent your supply voltage is now correct.